1. Field of the Invention
The present invention relates to an apparatus for and method of recording information on a recording medium that enables additional recording of information thereon.
2. Description of the Related Art
A write once (WO) type optical disk and rewritable (RW) type optical disk are recording media that enable additional recording of information thereon. The WO type disk is a disk that enables information to be written only once at the same portion thereof. The RW type optical disk is a disk that enables information to be written many times at the same portion thereof.
In an information recording apparatus that writes information data onto a disk enabling additional recording of information, when information data is written onto a disk, a write clock signal is produced. The information recording apparatus then writes information data onto the disk while making a synchronization (e.g., bit synchronization) between the thus-produced and stable write clock signal having a predetermined frequency and the writing operation of writing information data onto the disk. This write clock signal in general is produced by a reference clock generator such as a crystal oscillator enabling the independent generation of an oscillation output.
However, in a case where additionally recording new information data onto the disk in which information data is already partly or locally written, in such a way that the new information data is written successively to this already written information data, there is the possibility that the write clock signal that was used for recording of the already written information data and the write clock signal that is used for recording of the new information data will fall out of phase.
In this case, when performing an operation of reading information data from a disk on which new information data has been written successively to the already written information data, it is difficult to reproduce a synchronization clock signal at or around a portion of connection between the preceding and the succeeding information data. If the synchronization clock signal cannot be reproduced correctly, the information data cannot be read correctly.
Especially, if information data is firstly written onto the disk by a information recording apparatus, and thereafter, another information data is successively written onto the same disk by a different information recording apparatus, the former information data and the later information data are recorded according to two different write clock signals, respectively. Even if the types of those information recording apparatus are the same, the write clock signals generated in the respective information recording apparatuses are actually different from each other not only in phase but also in frequency.
In order to reproduce a synchronization clock signal to be used for reading information data, a PLL (Phase Locked Loop) circuit is used. if preceding data and succeeding data are written onto the disk according to different write clock signals, respectively, the synchronizing operation of the PLL circuit is largely disturbed at or around the portion of connection between such preceding data and succeeding data, when reproducing these data. As a result of this, there is the possibility that a decoder for performing decoding processing of the read data according to the synchronization clock signal of it will inconveniently make an erroneous detection of various data items in the read data.
Also, generally, information data to be written onto a disk is divided into information blocks each having a prescribed size, and a particular synchronization signal is added to each of the information blocks. Accordingly, when reproducing information data from the disk, it is also possible to establish a synchronization based on the particular synchronization signal added to each information block, as well as to make a bit synchronization such as that mentioned above. However, such a particular synchronization signal is also inherently one which has been recorded in the disk with a timing based on the write clock signal. Accordingly, if a preceding particular synchronization signal and succeeding particular synchronization signal are written onto the disk using write clock signals different from each other in phase or frequency, the periodic continuity can not be still obtained.
For example, there is a case where the interval between a particular synchronization signal added to a rearmost region of the preceding information block and a particular synchronization signal added to a foremost region of the succeeding information data irregularly varies due to the difference between the write clock signals. In this case, there is the possibility that when performing reproduction, such difference will be followed by a failure of detection or an erroneous detection.
An object of the present invention is to provide an information recording apparatus and method which can control recording of information so as to enable written data and its immediately succeeding additionally written data to be smoothly successively reproduced without disturbing the synchronizing operation of synchronizing read data at the time of reproduction.
An information recording apparatus in accordance with the present invention is an apparatus for recording first information onto a recording medium, successively to second information that has been already recorded on the recording medium. Both the first and second information are divided into a plurality of blocks each having a predetermined length. Each of the plurality of blocks includes a synchronization signal. The synchronization signal is located at a predetermined position in each of the plurality of blocks. A plurality of pre-pits are pre-formed on the recording medium at intervals of the predetermined length or an integer times the predetermined length. A reference signal is pre-recorded on the recording medium. The reference signal has a predetermined frequency.
The information recording apparatus includes: a write clock signal generating device for generating a write clock signal on the basis of the reference signal obtained from the recording medium; a pre-pit detecting device for detecting the plurality of pre-pits from the recording medium and outputting a pre-pit signal at a first timing, which is equal to a timing that each of the plurality of pre-pits is detected; a synchronization signal generating device for generating the synchronization signal and outputting the synchronization signal at a second timing, which is synchronized with the write clock signal, and which is set so as to place the synchronization signal at the predetermined position in each of the plurality of blocks; a time relationship detecting device for detecting a time relationship between the pre-pit signal and the synchronization signal; a shifting device for shifting a phase of the write clock signal so as to make the detected time relationship equal to a predetermined time relationship; and a recording device for recording the first information and the synchronization signal onto the recording medium in accordance with the second timing.
In this apparatus, when the first information is recorded onto the recording medium, successively to the second information, the write clock signal is used. This write clock signal is generated on the basis of the reference signal which is pre-recorded on the recording medium. Therefore, the write clock signal which has constant characteristics, e.g. a constant frequency, can be always generated from one recording medium. As a result of this, the first information can be recorded successively to the second information by using the same write clock signal as that used when the second information was recorded. This contributes to the successive reproduction of the second information and first information.
Further, when the first information is recorded successively to the second information, the pre-pit is detected from the recording medium. In response to the detection of the pre-pit, the pre-pit signal is generated and output at the first timing. The first timing is equal to the timing that the pre-pit is detected. Further, the synchronization signal is generated and output at the second timing. The second timing is synchronized with the write clock signal, and set so as to place the synchronization signal at the predetermined position in each of the plurality of blocks.
A time relationship between the pre-pit signal and the synchronization signal is then detected, and the phase of the write clock signal is shifted so as to make the detected time relationship equal to a predetermined time relationship. Namely, since the second timing is synchronized with the write clock signal, shifting the write clock signal causes shifting the second timing, so that the timing that the synchronization signal is output is also shifted. Thus, the predetermined time relationship is established between the pre-pit signal and the synchronization signal. As a result of this, the phase of the synchronization signal always become constant, because the pre-pits are pre-formed on the recording medium at intervals of the predetermined length or an integer times the predetermined length.
Thus, the timing that the synchronization signal is output, i.e., the second timing, is set by using the write clock signal that has an always constant frequency based on the reference signal pre-recorded on the recording medium and by using the pre-pit signal that is always detected at the constant timing based on the pre-pits pre-formed on the recording medium. Therefore, it is possible to set the period and phase of the synchronization signal at a constant period and a constant phase, each time the additional recording is carried out. In accordance with this second timing, the first information and the synchronization signal are recorded successively to the second information. Accordingly, it is possible to control recording of information so as to enable first information and second information to be smoothly successively reproduced without disturbing the synchronizing operation of synchronizing read data at the time of reproduction.
The time relationship between the pre-pit signal and the synchronization signal may be detected by detecting a difference between the first timing and the second timing, and then shifting the phase of the write clock signal so as to remove the difference between the first timing and the second timing.
An eliminating device for eliminating jitters from the reference signal on the basis of the pre-pit signal may be added to the aforementioned information recording apparatus. By adding this device, the stability and accuracy in frequency of the write clock signal can be improved.
The elimination of jitter may be carried out by reducing a phase difference between the reference signal and the pre-pit signal such that the phase difference is within a range of a predetermined tolerance, by shifting a phase of the reference signal.
The above-stated object can be also achieved by an information recording method in accordance with the present invention. The information recording method is a method of recording first information onto a recording medium, successively to second information that has been already recorded on the recording medium. The method has the processes of: generating a write clock signal on the basis of the reference signal obtained from the recording medium; detecting the plurality of pre-pits from the recording medium and outputting a pre-pit signal at a first timing, which is equal to a timing that each of the plurality of pre-pits is detected; generating the synchronization signal and outputting the synchronization signal at a second timing, which is synchronized with the write clock signal, and which is set so as to place the synchronization signal at the predetermined position in each of the plurality of blocks; detecting a time relationship between the pre-pit signal and the synchronization signal; shifting a phase of the write clock signal so as to make the detected time relationship equal to a predetermined time relationship; and recording the first information and the synchronization signal onto the recording medium (1) in accordance with the second timing.
Thus, the timing that the synchronization signal is output, i.e., the second timing, is set by using the write clock signal that has an always constant frequency based on the reference signal pre-recorded on the recording medium and by using the pre-pit signal that is always detected at the constant timing based on the pre-pits pre-formed on the recording medium. Therefore, it is possible to set the period and phase of the synchronization signal at a constant period and a constant phase, each time the additional recording is carried out. In accordance with this second timing, the first information and the synchronization signal are recorded successively to the second information. Accordingly, it is possible to control recording of information so as to enable first information and second information to be smoothly successively reproduced without disturbing the synchronizing operation of synchronizing read data at the time of reproduction.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.